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4. Database Design Principles > 4.5. Second Normal Form

Second Normal Form

Intuitively, a table scheme T is in second normal form if all of the strictly informational attributes (attributes that do not belong to any key) are attributes of the entities in the table scheme, and not of some other class of entities. In other words, the informational attributes provide information specifically about the entities in this entity class and not about some other entities.

Let us illustrate with an example. Consider a simplified table scheme designed to store house addresses. One possibility is:

{City,Street,HouseNumber,HouseColor,CityPopulation}

The CityPopulation attribute is out of place here because it is an attribute of cities, not house addresses. More specifically, CityPopulation is strictly an informational attribute (not for identification of houses), but it gives information about cities, not house addresses. Thus, this table scheme is not in second normal form.


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